1. Field of the Invention
The present invention relates to a semiconductor device in which a semiconductor element is mounted to an insulating circuit board, and more particularly, to a semiconductor device whose reliability of mounting is improved by means of improving a joint between a semiconductor element and an insulating circuit board, to thereby alleviate stress developing in a solder joint formed on each of external electrodes of the semiconductor device.
2. Background Art
FIG. 4 is a cross-sectional view showing a conventional semiconductor device in which a semiconductor element is mounted on the insulating circuit board.
As shown in FIG. 4, in the conventional semiconductor device, a semiconductor element 10 is mounted face-down on a circuit board 1 through use of an adhesive layer 5. An element electrode 11 is connected to a board electrode 4 provided on the lower surface of the circuit board 1 via an opening hole 2 formed therein and through use of a wire 12. The joint between the element electrode 11 and the board electrode 4 is sealed with resin 6. External electrodes 3 are provided on the lower surface of the circuit board 1. Each of the external electrodes 3 is fixedly mounted on the circuit board 1 via a solder joint 31 and on a module board 200 via a solder joint 32.
While the semiconductor element 10 is placed face-down on the insulating circuit board 1, the semiconductor element electrode 11 and a board electrode 4 provided on the lower surface of the insulating circuit board 1 are electrically interconnected by way of the opening hole 2 of the insulating circuit board 1. In the semiconductor device in which the joint between the semiconductor element electrode 11 and the board electrode 4 is sealed with resin, an adhesive layer 5 for bonding together the semiconductor element 10 and the insulating circuit board 1 is equal in size with the semiconductor element 10.
The semiconductor device 100 having such a configuration is fixedly mounted on the module board 200 via the external electrodes 3.
FIG. 5 is a cross-sectional view showing another conventional semiconductor device. The semiconductor device shown in FIG. 5 corresponds to the semiconductor device 100 shown in FIG. 4, in which the surrounding regions of the side surfaces of the semiconductor element 10 are additionally coated with sealing resin 7 so as to assume a flange structure. More specifically, the semiconductor device corresponds to the conventional semiconductor device shown in FIG. 4, in which the side surfaces of the semiconductor element 10 are sealed with resin so as to assume a flange structure.
In the conventional semiconductor devices shown in FIGS. 4 and 5, the resin of the adhesive layer 5 used for bonding the semiconductor element 10 to the insulating circuit board 1 is substantially equal in size with the semiconductor element 10. Stress due to a difference in thermal expansion coefficients of the constituent members of the semiconductor device 100 is exerted on the external electrodes 3 provided on the outermost periphery of the insulating circuit board 1, thereby resulting in a tendency toward a reduction in the reliability of packaging of the semiconductor device 100.
Further, there has recently been posed the task of prolonging the life of solder joints in a temperature cycle test, where a semiconductor device is mounted on a module board.
The present invention has been conceived to solve such a problem in the background art and is aimed at providing a semiconductor device which has improved joints between an insulating circuit board and a semiconductor element and improved reliability of mounting and which attains prolonged life of solder joints in a temperature cycle test to which the semiconductor device is subjected while being mounted on the module board.